you should check with the airline company, as it is their decision if they let you onboard or not.
When I went to Colombia few years ago, I bought a one way ticket (from London via Madrid) with Avianca, on their website. No problem to buy it online and no problem to get to Madrid.
But when we got to Madrid, at the boarding gate, we were refused entry to the plane, because we did not have a flight out! Showing them the docs of the shipping company to prove we were going to exit by land was useless, they wanted a plane ticket out.
They said it was the rules in Colombia. That is probably not true, I think the fact is, if you are refused entry to the final destination, the airline has to bring you back.
Don't get caught out, check with the airline direct.